1. Field of the Invention
The present invention relates to an electronic-component-mounting board including: a high-heat-dissipation substrate including a metal plate and a circuit pattern formed on a thin insulation layer disposed on an upper surface of the metal plate; an electronic component mounted on the high-heat-dissipation substrate; and one external-connection terminal which is disposed on the high-heat-dissipation substrate and provides electrical connection between the electronic component and an external device.
2. Description of Related Art
In wiring boards for mounting electronic components, such as light-emitting diodes, that generate a relatively large amount of heat, appropriate measures for heat dissipation must be taken. For example, wiring boards are already known in which a metal substrate having high-thermal conductivity is used to mount electronic components such as light-emitting diodes elements which are electrically connected to a circuit pattern formed on an upper surface of the metal substrate. In one known example of a substrate having high heat dissipation characteristics, a thin insulating layer is provided on the upper surface of a metal plate, and a predetermined circuit pattern is formed on the insulating layer (see, for example, Japanese Design Registration No. 1261413).
FIG. 6 is a perspective view illustrating an example of an electronic-component-mounting board previously proposed by the present applicant. As shown in FIG. 6, a conventional electronic-component-mounting board 1 is composed of: a high-heat-dissipation substrate 2 in which a metal plate 2a, such as an aluminum plate, having high-thermal conductivity is used; a light-emitting unit 3 serving as an electronic component and mounted on a substantially central portion of the high-heat-dissipation substrate 2; and external-connection terminals 4 which are disposed on opposite end portions of the high-heat-dissipation substrate 2 to provide electrical connection to an external device (not shown).
The high-heat-dissipation substrate 2 has a predetermined circuit pattern (not shown) formed on the upper surface of the metal plate 2a with an insulating layer 5 therebetween. The light-emitting unit 3 is composed of: a plurality of light-emitting diode elements 6 disposed on the high-heat-dissipation substrate 2; and a light-transmitting resin 7 that encapsulates the light-emitting diode elements 6.
Conventionally, a female connector is used as each of the external-connection terminals 4. By fitting a male connector (not shown) in the female connector, electric power is supplied from the outside to the light-emitting-diode elements 6 through the circuit pattern.
However, when a female connector is used as each of the external-connection terminals 4, its connection is made through engagement with a male connector, and therefore electrical reliability in a long-term use is problematic. Moreover, the above connectors may serve as an obstacle to miniaturization and thickness reduction and are also expensive.
In view of the above, it is conceivable that a lead wire is directly soldered and connected to the circuit pattern of the high-heat-dissipation substrate avoiding use of the conventional connectors. However, in this case, during the soldering of the lead wire to a circuit pattern disposed on a thin insulating layer disposed on the high-heat-dissipation substrate, necessary heat for soldering easily escapes to the metal plate constituting the high-heat-dissipation substrate, and therefore, an excessive amount of time is required to increase the temperature of the lead wire junction to the melting point of the solder. On the other hand, if the entire electronic-component-mounting board is heated in order to reduce the time required to increase the temperature of the lead wire junction to the melting point of the solder, other components such as the electronic-component are overheated and damaged.